Focusing technique plays a crucial role among all optical devices and gear. The demand of the focusing technique lies in the varied distance between the camera lens and the light sensors (negative {grave over ( )} CCD {grave over ( )} CMOS) of optical devices and the photographed objects. For the clear imaging of a photographed object on a light sensor, the distance between the optical center of the lens and the light sensor needs to be adjusted, and such a step is the so-called focusing. Modem approaches mostly adjust focus by moving the camera lens or the lens thereinside.
Please refer to FIG. 1, which shows a schematic diagram of focusing steps of an optical device in the prior art. The optical device 1 includes a lens 11 and a light sensor 10, and the optical device 1 needs to be focused on consecutive planes from a first plane P1 to a third plane P3. To simplify the diagram, only three planes are shown therein, which includes the first plane P1, a second plane P2, and the third plane P3, wherein the first plane P1 is the one farthest to the optical device 1; the third plane P3 is the one closest to the optical device 1, and the second plane P2 is the one in the middle of the first plane P1 and the third plane P3. These three planes are used to describe the change of light path in response to different planes.
The problem for focusing in the prior art is that each lens has a certain weight, and it is a heavy work to move more than one lenses or even to move a whole lens assembly. When a user does not need to focus the optical device frequently, such a focusing method is normally appropriate. As to FIG. 1, however, a repetitive focusing is required. That is, a photographed object can be located from the first plane P1, the second plane P2 to the third plane P3, then the process starts over from the first plane P1. Consequently, in the focusing method of the prior art, it takes great effort for the lens 11 to focus the photographed objects located from the first plane P1 to the third plane P3. Furthermore, when the positions of the first plane P1, the second plane P2, and the third plane P3 are fixed, and a first object distance D1 between the lens and the first plane P1, a second object distance D2 between the lens and the second plane P2, and a third object distance D3 between the lens and the third plane P3 are also fixed, the focusing step can be preset without active or passive focus. Although the lens 11 can be moved to the preset locations, it remains problematic in the steps of “starting to move”, “moving”, and “ceasing to move”. In the “starting to move” step, the focusing driving component needs to overcome the static friction of the focusing device. In the “moving” step, the kinetic friction of the focusing device needs to be overcome. In the “ceasing to move” step, the moving lens and lens assembly need to be stopped, i.e. the kinetic energy thereof needs to be counterbalanced. Therefore, the focusing driving component and the focusing device are mostly burdened in the “starting to move” and “ceasing to move” steps. The simplest way to overcome the mentioned problem is to use durable or expensive material to manufacture an enlarged focusing device, and thus a more powerful focusing driving component is necessary. Nevertheless, in this way, the optical device 1 would be bigger and heavier, and the cost thereof would be higher. After such a huge change in the design, the existing components and materials are useless, causing the wastage of resources.
Based on the above, in the field of auto-focusing, a resolution regarding the method, technique, and the equipment is required to focus rapidly, and to economize the use of resource and cost by utilizing existing components and materials.